For centuries the social and political organization of many Iraqi Arabs has centered on the tribe. Socially, tribes were divided into related sub-tribes, which further divided into clans, and then into extended families. Seventy-five percent of Iraq's estimated 26 million people are a member of a tribe. They are more strongly bound by these tribal ties and a strict honor code than by ethnic background or religion. This report describes the political orientation of several Iraqi Arab tribes, including the Shammar, Dulaym, and Jibur tribes. This report will be updated as warranted. For further information on Iraq and U.S. policy, see CRS Report RL31339, Iraq: Post-Saddam Governance and Security, by Kenneth Katzman.